PEPSIN DIGESTION. 449 



55 C. (HASEBROEK l ). For information in regard to the different pro- 

 teoses and peptones which are formed in pepsin digestion see pages 127 

 to 136. 



Action of Pepsin-Hydrochloric Acid on Other Bodies. The gelatin- 

 forming substances of the connective tissue, of the cartilage, and of the 

 bones, from which last the acid dissolves only the inorganic substances, 

 is converted into gelatin by digesting with gastric juice. The gelatin is 

 further changed so that it loses its property of gelatinizing and is con- 

 verted into gelatoses and peptone (see page 119). True mucin (from the 

 submaxillary) is dissolved by the gastric juice, yielding substances similar 

 to peptone, and a reducing substance similar to that obtained by boiling 

 with a mineral acid. Mucoids from tendons, cartilage, and bones dissolve, 

 according to POSNER and GiES, 2 in pepsin-hydrochloric acid, but leave 

 a residue which amounts to about 10 per cent of the original material 

 and which, as it seems, consists in great part, if not entirely, of a com- 

 bination of proteid with glucothionic acid (Chapters VII and VIII). The 

 solution contains primary and secondary mucoproteoses and mucopep- 

 tones. The former contain glucothionic acid, but the latter do not. 

 Elastin is dissolved more slowly and yields the above-mentioned sub- 

 stances (page 116). Keratin and the epidermal formations are insoluble. 

 The nucleins are dissolved with difficulty, and the cell nuclei, therefore, 

 remain in great part undissolved in the gastric juice. The animal cell- 

 membrane is, as a rule, more easily dissolved the nearer it stands to elastin, 

 and it dissolves with greater difficulty the more closely it is related to 

 keratin. The membrane of the plant-cell is not dissolved. Oxy hemoglobin 

 is changed into hoimatin and protein, the latter undergoing further 

 digestion. It is for this reason that blood is changed into a dark-brown 

 mass in the stomach. The gastric juice does not act upon fat, but, on 

 the contrary, dissolves the cell-membrane of fatty tissue, setting the 

 fat free. Gastric juice has no action on starch or the simple varieties 

 of sugar. The statements in regard to the ability of gastric juice to 

 invert cane-sugar are very contradictory^ At least this action of the 

 gastric juice is not constant, and if it is present at all it is probably due 

 to the action of the acid. 



Pepsin alone, as above stated, has no action on proteins, and an acid of the 

 intensity of the gastric juice can only very slowly, if at all, dissolve, coagulated 

 albumin at the temperature of the body. Pepsin and acid together not only 

 act more quickly, but qualitatively they act otherwise than the acid alone, at 

 least upon dissolved protein. This has led to the assumption of the presence of 

 a pepsin-hydrochloric acid whose existence and action are only hypothetical. 

 As pepsin digestion, it seems, yields finally the same products as the hydrolytic 

 cleavage with acids, we can say for the present only that this enzyme acts like 

 other catalysts in very powerfully accelerating a process which would also 

 proceed without the catalytes. 



1 Zeitschr. f. physiol. Chem., 11. 2 Ainer. Journ. of Physiol., 11. 



